Because reconnaissance CSEM surveys must be designed in the absence of any information about specific targets, that being what is meant by the term “reconnaissance,” methods used for designing traditional target-oriented CSEM surveys are inapplicable. In addition, because the interpretational objectives and prior information are different from target-oriented CSEM surveys, a different interpretation approach is needed.
Target-oriented CSEM surveys are currently directed towards one or more specific targets that have been identified and characterized using prior information, such as 3D seismic data. Design and interpretation of these surveys is guided by this prior information (Kong et al., “Seabed logging: A possible direct hydrocarbon indicator for deepsea prospects using EM energy, Oil and Gas Journal, 30-38 (May 13, 2002)). In reconnaissance CSEM surveying, the specific target parameters may not be available and usually only general geological information is known. The few attempts at designing reconnaissance CSEM surveys concentrated on improving resolution and accuracy. See Maurer et al., “Optimized and robust experimental design: a non-linear application to EM sounding,” Geoph. J. Int. 132, 458-468 (1998); and Singh et al., “Effective skin depth with a local source and its application to survey design and data interpretation,” 72nd Ann. Internat. Mtg: Soc. of Expl. Geophys., 684-687 (2002). The equipment vendors offer cheaper tools to cover large areas (usually in regular grid) at reduced costs. See Eaton et al., “NEWTEM—A novel time-domain helicopter electromagnetic system for resistivity mapping,” 72nd Ann. Internat. Mtg: Soc. of Expl. Geophys., 1-4 (2002). Other writers suggested an approach to survey design based on global minimization where the objective function includes the measure of optimal resolution and penalizes the survey cost through the number of required measurements (Maurer et al., “Geophysical survey design: Get the most for the least!” 68th Ann. Internat. Mtg: Soc. of Expl. Geophys., 78-81 (1998)). There is a need for a method that can evaluate a proposed reconnaissance survey of a particular design, and allow comparison of different survey designs on an expected value basis. The present invention satisfies this need.